Maybe anyone can contest a will, but that doesn't mean they'll be successful.
I've heard of wills that say that anyone who contests it will be disinherited, but I don't know whether that has been test in court or not. My own will says that anyone who contests it will have their bequest reduced to $1 and the remainder of their previous bequest distributed proportionately to the other heirs. My lawyer says it will hold up, but I guess I will never know.
Either way, it's better to have a will you think may be contested that to not have one at all. If you can afford it, it is often better to give gifts to your loved ones before your death. No one can contest a gift given during your lifetime, unless they claim it was given under duress or undue influence.
There will always be people with their hands out, ready to take whatever they can from whomever they can.